I use and love Talkatone, I tried GV Phone because I use it on my old Android (I like bragging that I can have my number on multiple phones :P ) and its a lot more simpler, but not necessarily better.
You can't send MMS's with GV Phone, hence I switched back to Talkatone.

Why would you want that? I'm sure there's a way you can add more than one GV account to Talkatone, although it seems pointless to have to manage two numbers for two purposes they both could do individually...

Edit: You CAN have multiple GV accounts linked to talkatone, although you need to pay for Talkatone Premium, which also removes ads, but is subscription based, so it'll cost you a fair bit.

Skype and Talkatone provide all of the quality, functionality, and value that we need. But if we have stickler for options and want to investigate the playing field further, here are some other VoIP apps:
1. Fring
2. Line2